EP0072784A2 - Schaltungsplatte zur Anwendung in einem kapazitiven Tastenfeld - Google Patents

Schaltungsplatte zur Anwendung in einem kapazitiven Tastenfeld Download PDF

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Publication number
EP0072784A2
EP0072784A2 EP82870044A EP82870044A EP0072784A2 EP 0072784 A2 EP0072784 A2 EP 0072784A2 EP 82870044 A EP82870044 A EP 82870044A EP 82870044 A EP82870044 A EP 82870044A EP 0072784 A2 EP0072784 A2 EP 0072784A2
Authority
EP
European Patent Office
Prior art keywords
circuit board
plates
plate
capacitive
pair
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP82870044A
Other languages
English (en)
French (fr)
Other versions
EP0072784A3 (de
Inventor
George P. English
Mark E. Reisenauer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Arris Technology Inc
Original Assignee
Arris Technology Inc
General Instrument Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arris Technology Inc, General Instrument Corp filed Critical Arris Technology Inc
Publication of EP0072784A2 publication Critical patent/EP0072784A2/de
Publication of EP0072784A3 publication Critical patent/EP0072784A3/de
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/965—Switches controlled by moving an element forming part of the switch
    • H03K17/975—Switches controlled by moving an element forming part of the switch using a capacitive movable element
    • H03K17/98—Switches controlled by moving an element forming part of the switch using a capacitive movable element having a plurality of control members, e.g. keyboard

Definitions

  • This invention relates generally to capacitive keyboards and more particularly to a circuit board having conductive plates mounted thereto for use in a capacitive keyboard.
  • keyboards In the past, various types of keyboards have been used on computer terminals and the like for entering data into a computer.
  • the type of keyboards is generally designated by the particular switching mechanism which is used in its keyswitches. Mechanical switches providing electrical contact between conductive electrodes, reed switches utilizing a magnetic field to close conductive electrodes, and Hall-effect switches have all been used in past keyboard designs.
  • Another type of keyswitch used in keyboards is known as the capacitive type. In such "capacitive keyboards", the actuation of a keyswitch operates to change the capacitance of two or more corresponding plates of a capacitor. Each separate keyswitch has its own set of plates. The capacitor plates are usually located on the surface of a printed circuit board, the plates being formed during the conventional etching process used in the manufacture of such boards.
  • Conventional printed circuit boards are manufactured from a base material comprising a non-conductive substrate and a copper layer coated with a photosensitive material known as a "photoresist".
  • the copper side of the board is photographically exposed to a negative of the pattern which is to be placed on the finished circuit board.
  • the pattern contains areas where copper is to remain on the finished product and other areas where copper is to be removed from the printed circuit board.
  • light which is transmitted through the negative hardens the chemical photoresist layer. In areas where no light is transmitted, the resist layer is not hardened.
  • the circuit board is placed into an etching solution which removes the copper layer from the areas which were not exposed to light during the exposure process.
  • the remaining circuit board contains conductive copper traces only in the desired areas. Holes may be drilled into the remaining traces and through the circuit board at desired locations. Electronic components may then be mounted to the non-copper side of the circuit board with their leads inserted into the holes and being soldered to corresponding copper traces.
  • the capacitive plates were formed from copper areas which were left on the copper side of the printed circuit board. As a result, the copper areas forming the capacitive plates were- interspersed on the same side of the circuit board with the copper traces forming the conductors for the associated electronic circuitry.
  • This design caused several problems. One problem was that the amount of area on the printed circuit board available for circuit conductors was substantially reduced due to the space requirements for the capacitive plates. The number of conductors on a given area of circuit board is known as "trace density". By using up space that would otherwise be available for conductive traces, the presence of such capacitive plates adversely affected the trace density of prior art circuit boards.
  • a third problem which occurs with prior art capacitive keyboards relates to the placement of electronic components on the circuit board.
  • capacitive keyboards the actuation of a key by a keyboard operator causes the base of a plunger connected to the key to come into close proximity to the capacitive plates.
  • the side of the circuit board containing the capacitive plates must therefore face upward, toward the operator and the keyboard keys.
  • the conductive traces also face upward.
  • the electronic components mounted to the non-copper side of the board therefore face downwardly and are more susceptible to damage than they would be if they were mounted on top of the board.
  • Such a keyboard should utilize a circuit board which eliminates the need to protect the capacitive plates from becoming coated with solder during the flow soldering process.
  • the circuit board should also enable the electronic components mounted thereon to be placed on the same side of the board which contains the capacitive plates. Additionally, it would be beneficial if such a circuit board reduced the need for separate wire jumpers.
  • This invention relates to such a keyboard.
  • the capacitive keyboard of the present invention utilizes a printed circuit board having first and second sides.
  • the circuit board contains a plurality of holes which are drilled therethrough and into which electronic components and the like can be mounted.
  • One side of the circuit board contains a plurality of electrically conductive traces.
  • the other side of the circuit board has at least one pair of thin conductive plates mounted thereto and parallel therewith. Each plate has at least one terminal protruding therefrom which extends into one of the holes in the circuit board to connect with a corresponding trace on the other side of the circuit board.
  • Actuating means are mounted in overlaying relation to the pair of conductive plates. When actuated, the actuating means causes the electrical capacitance between the plates to change
  • the above described configuration is advantageous in that the conductive plates are not present on the same side of the printed circuit board as the conductive traces forming the circuit. Thus, the problems of trace density, flow soldering, electronic component placement, and wire jumpers are reduced.
  • the present invention relates to capacitive keyboards of the type having a circuit board 10 (shown in Fig. 2) on which keyswitches 21 through 99 are mounted. Such keyboards are used for the entry of data in various computer oriented applications.
  • a typical keyswitch 61 comprises a key top 101 which is affixed to a plunger 103.
  • a spring 105 provides a return force to the plunger after the key top 101 has been momentarily depressed. Return spring 105 sits on housing 113, providing a spring force directed away therefrom. Housing 113 encloses an actuator assembly which serves to change the capacitance of two series capacitors formed by capacitive plates 121 and 131 as described below.
  • the actuator assembly comprises a metal plate 107 which is affixed to plunger 103.
  • One way to affix metal plate 107 to plunger 103 is to use resilient tabs 115 onto which metal plate 107 can be snapped.
  • a foam pad 109 is affixed to metal plate 107 with a suitable adhesive.
  • Tne actuator assembly is completed by mounting a mylar sheet 111 to the outer surface of foam pad 109. Mylar sheet 111 is metalized on one side, the metalized layer 110 being adjacent foam pad 109.
  • the surface of mylar facing capacitive plates 121 and 131 is non-conductive.
  • Key switch 61 is mounted to circuit board 10 by screw 128 which protrudes through a mounting hole 127 in the circuit board and into threaded mounting hole 130 in switch housing 113. Notch 129 is provided in capacitive plate 131 to allow screw 128 to pass thereby without interference. Those skilled in the art will appreciate that any other of a variety of mounting schemes can alternatively be used.
  • FIG. 2 shows an exploded view of the mounting of capacitive plates 121 and 131 thereon.
  • Capacitive plate 121 has tabs 123 and 125 which protrude through corresponding holes 122 and 124 in circuit board 10.
  • Plate 121 is mounted to circuit board 10 by soldering tabs 123 and 125 to respective circuit traces on the opposite of circuit board 10.
  • pin 123 of plate 121 corresponds with circuit trace 322 on the other side of the circuit board.
  • pin 125 corresponds to circuit trace 324.
  • Pins 123 and 125 can be soldered to traces 322 and 324 in a conventional flow soldering process which occurs after all of the capacitive plates and associated electronic components are mounted onto the component side of circuit board 10.
  • Outer capacitive plate 131 contains pins 133 and 135 which correspond with holes 132 and 134 in circuit board 10. These pins are also soldered to corresponding traces 332 and 334 on the opposite side of circuit board 10.
  • Capacitive plates 121 and 131 are formed from a conductive metal or metal alloy.
  • One alloy that can be used for these plates contains copper and nickel and is known in the trade as CDA alloy #725.
  • CDA alloy #725. Those skilled in the art will appreciate that other metals and/or alloys may be used with equally goods results.
  • the capaoitive plates may be formed in any number of ways. One way is to chemically etch the plates in strips from the base metal material. After etching, the mounting pins are bent into shape and each individual plate is severed from the strip of plates and mounted into the circuit board. The use of the chemical etching process gives nicely rounded edges which facilitates the machine handling of the strips of plates in the automated assembly of circuit boards.
  • the capacitive plates 121, 131 comprise an outer plate 131 of generally square shape having a generally square opening in the center thereof and an inner plate 121 of generally square shape within the perimeter of the opening in the outer plate.
  • outer plate 131 of generally square shape having a generally square opening in the center thereof and an inner plate 121 of generally square shape within the perimeter of the opening in the outer plate.
  • other shapes such as semi-circles or rectangular strips may alternatively be used.
  • the pair of conductive plates 121, 131 serves, in conjunction with the metalized mylar sheet 111 on the actuator assembly, to form a pair of series connected capacitors.
  • the metalized mylar sheet 111 which is present on the actuator assembly is common to both of the separate capacitors and serves as the series interconnect therebetween.
  • Depressing a key on the keyboard brings the metalized mylar sheet 111 into close proximity to the pair of plates 121, 131 on the circuit board 10. This alters the capacitance of the series capacitors.
  • it is possible to determine whether or not a key has been pressed by placing a voltage transition across the pair of plates 121, 131 on the circuit board 10 and measuring the resultant current pulse therethrough. If the keyswitch has been actuated, the current measurement will indicate one value of capacitance. If the keyswitch has not been actuated, another value of current will be detected.
  • key switch 61 comprises a key top 201 mounted to a plunger 203.
  • Spring 205 provides the return force after key top 201 has been momentarily depressed.
  • Spring 205 acts against housing 213.
  • Housing 213 contains the key switch actuator assembly which comprises a metal disc 207 that has been snapped onto resilient locking tabs 215.
  • Actuator disc 207 contains fingers 209 and 211 which extend therefrom in spring loaded relation thereto. Fingers 209 and 211 act against capacitive plate 221 to provide a downward force thereto when key top 201 is depressed.
  • Capacitive plate 221 extends, in its non-depressed condition, upwardly at an angle a from circuit board 10 to which it is mounted by pins 223 and 225. Plate 221 exerts a spring force upward from circuit board 10 which is determined by the metal material forming the plate along with the geometry of lever arms 220.
  • a second capacitive plate 231 is mounted to circuit board 10 by pins 233 and 235.
  • a non-conductive coating 230 is applied to capacitive plate 231 to electrically insulate it from capacitive plate 221 when the plate are pressed together.
  • Coating 230 may be any insulating material, such as a plastic based paint which can be easily applied to the surface of plate 231. In operation, depressing a key on the keyboard brings capacitive plate 221 into close proximity with capacitive plate 231. This alters the capacitance between capacitive plates 221, 231.
  • the design of the actuator assembly shown in the capacitive keyswitch of Figures 5 and 7 provides a "linear feel" to the keyboard operator such that the amount of force required to actuate the keyswitch is contant throughout the downward travel of the key top.
  • the linear feel is advantageous in that it provides a highly marketable keyboard.
  • a capacitor is formed from the conductive plates mounted on circuit board 10.
  • one capacitor exists; namely, that formed from capacitive plates 221 and 231 which have dielectric coating 230 therebetween.
  • two separate capacitors are formed which are connected in series.
  • capacitive pads 121 and 131 are coupled in series relation by metalized mylar sheet 111 which forms a third capacitive plate.
  • one of the series capacitors in the embodiment of Figure 2 comprises inner capacitive plate 121 in parallel relation with metalized layer 110 having dielectric mylar 111 therebetween.
  • the second series capacitor is formed from outer capacitive plate 131 in generally parallel relation to metalized layer 110 having dielectric mylar 111 therebetween.
  • a change of capacitance will result between the capacitive plates of a given keyswitch when that keyswitch is actuated.
  • keyswitch 61 ' is actuated in Figure 2
  • the change of capacitance will arise between inner and outer capacitive plates 121 and 131.
  • This change may be detected by causing a voltage transition to occur across capacitive plates 121 and 131 and measuring the resulting current pulse therethrough. If the keyswitch is in the actuated position when the voltage transition occurs, one value of current will be measured. If the keyswitch is in the non-actuated position, another current value will be measured.
  • the voltage transition will be developed across capacitive plates 221 and 231 and the current therethrough will be measured. It is noted that in a keyboard constructed in accordance with the present invention, no electrical connection is required to be made to the keyswitch actuator itself. Actuation of the keyswitch causes a change in capacitance across conductive plates which are mounted to a fixed circuit board.

Landscapes

  • Input From Keyboards Or The Like (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)
  • Casings For Electric Apparatus (AREA)
  • Push-Button Switches (AREA)
EP82870044A 1981-08-19 1982-08-10 Schaltungsplatte zur Anwendung in einem kapazitiven Tastenfeld Ceased EP0072784A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US29434281A 1981-08-19 1981-08-19
US294342 1981-08-19

Publications (2)

Publication Number Publication Date
EP0072784A2 true EP0072784A2 (de) 1983-02-23
EP0072784A3 EP0072784A3 (de) 1983-10-19

Family

ID=23132999

Family Applications (1)

Application Number Title Priority Date Filing Date
EP82870044A Ceased EP0072784A3 (de) 1981-08-19 1982-08-10 Schaltungsplatte zur Anwendung in einem kapazitiven Tastenfeld

Country Status (3)

Country Link
EP (1) EP0072784A3 (de)
JP (1) JPS5840713A (de)
MX (1) MX151557A (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9600084B2 (en) 2014-01-09 2017-03-21 Synaptics Incorporated Methods and apparatus for capacitively detecting key motion and finger presence on keyboard keys

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3877029A (en) * 1973-03-09 1975-04-08 Magic Dot Inc Electronic keyboard
FR2366620A1 (fr) * 1976-09-30 1978-04-28 Becton Dickinson Co Touche capacitive pour un clavier
GB2060895A (en) * 1979-09-28 1981-05-07 Bfg Glassgroup Capacitive touch control switch panels and method of manufacturing them

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3877029A (en) * 1973-03-09 1975-04-08 Magic Dot Inc Electronic keyboard
FR2366620A1 (fr) * 1976-09-30 1978-04-28 Becton Dickinson Co Touche capacitive pour un clavier
GB2060895A (en) * 1979-09-28 1981-05-07 Bfg Glassgroup Capacitive touch control switch panels and method of manufacturing them

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9600084B2 (en) 2014-01-09 2017-03-21 Synaptics Incorporated Methods and apparatus for capacitively detecting key motion and finger presence on keyboard keys
US10148268B2 (en) 2014-01-09 2018-12-04 Synaptics Incorporated Methods and apparatus for capacitively detecting key motion and finger presence on keyboard keys

Also Published As

Publication number Publication date
JPS5840713A (ja) 1983-03-09
EP0072784A3 (de) 1983-10-19
MX151557A (es) 1984-12-13

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Inventor name: ENGLISH, GEORGE P.

Inventor name: REISENAUER, MARK E.

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Effective date: 20230522